The present proposal seeks to extend a previously developed and standardized protocol for psychophysiologic investigations of cardiovascular reactivity to populations of young adult Black and White subjects. Second, the influence of acute changes in sodium balance on selected measures of cardiovascular reactivity to laboratory stressors will be evaluated. Third, the relationships between psychosocial indicies and physiologic measurements and their influence on measures of cardiovascular reactivity will be investigated in Blacks and Whites. The project plans to recruit 370 subjects (125 Black males, 125 White males, 60 Black females, 60 White females) for a standardized laboratory stress protocol involving three active stressors (mental arithmetic, Stroop Color - Word Test, mirror drawing), two passive stressors (isometric handgrip and cold pressor) followed by a period of dynamic exercise. Prior to the protocol subjects will complete a number of psychosocial inventories to assess both home environment and psychological characteristics. A subset of these volunteers will be recruited for a hospitalization protocol which involves acute sodium loading by saline infusion and acute sodium depletion with furosemide. Subjects will experience an abbreviated stress protocol on two occasions during the hospitalization protocol. The long term goal of this research is to allow identification of quantifiable characteristics related to blood pressure control mechanisms which predispose otherwise healthy individuals to develop high blood pressure later in life. This is to be accomplished by ascertaining a large number of biobehavioral characteristics of Black and White subjects who are exposed to many different types of transient stress under controlled environmental conditions.